Forging machines are used for forging workpieces having a distinct longitudinal axis and a circular, square, rectangular or similar cross-section, and are provided with rams, usually four in number, which act on the workpiece radially and simultaneously and are fitted with tools. The tools, whose action is distributed around the workpiece and which usually form an enclosed space or opening for the workpiece in their inner stroke end position, permit spread-free deformation with correspondingly thorough forging. Economical use of these forging machines demands a high degree of flexibility, and for this reason the workpieces are basically produced with no connection of shape between the tool and workpiece and without a change of tool. Tools with a flat working surface are therefore used. The resulting cross-section, being enclosed by the tools in the stroke end position, has sides whose length corresponds to the tool width. Smaller enclosed cross-sections cannot be forged, the larger enclosed cross-sections can be forged only in an open calibre and therefore not completely.
To overcome this disadvantage, tools have been used which have a plurality of projecting working surfaces in the longitudinal direction of the workpiece, and which engage in gaps in adjacent tools in the manner of a comb (German Patent Publication AS No. 10 94 075). The minimum enclosed cross-section can differ from the maximum enclosed cross-section in the length of side by double the gap depth, with the workpiece space closed. This advantage, however, is attained at the expense of interruption of the flat working surfaces of the tools, and material is expelled into the gaps, to a greater degree, the greater is the deformation per stroke. For this reason such tools are used only for short-stroke forging machines, that is, machines which operate more by hammering than by pressing. Even when the gaps are only in the marginal areas of the tools, so that the tools have a continuous working surface in the region of the breadth of the smallest enclosed cross-section, there is still the disadvantage that undesirable markings or deformations occur in the marginal area on the larger cross-sections.
It is also known for the tools to be so arranged that the lateral surface of a tool bears on the working surface of the adjacent tool, so that the tools together form a closed calibre in any position. A prerequisite for this arrangement of tools is that the ram axes are parallel to the cross-section diagonals and the working surface of the tools is oblique relative to the ram axis (German Pat. No. 449 558, German Patent Application OS No. 19 53 123), or that, with ram axes approximately perpendicular to the working surfaces of the tools, the tools, which are guided by rods, and the ram and cylinder units must be pivotably connected to the machine frame and tools (German Utility Model 19 53 867, corresponding to U.S. Pat. No. 3,478,565). The required construction outlay, undesirable stressing of the components, wear-prone guides and in particular relative sliding of the tools and workpiece due to the oblique or oscillatory motion of the tools are serious drawbacks of forging machines of the type described above.